Analogue integrated circuits such as integrated power supply controllers are commonly trimmed at the wafer level to correct for parameter variations due to process variations. This generally employs the use of additional trimming pads within the wafer that are not bonded out. For this reason the trimming is generally performed before packaging (when the pads are accessible) but this has the disadvantage that trimmed parameters may change after encapsulation, for example due to stresses during the packaging procedure. It would therefore be advantageous if trimming could be carried out after packaging. This should reduce the errors in trimmed parameters arising due to packaging stresses.
One technique for programming a power supply controller is described in U.S. Pat. No. 6,388,853, which describes an arrangement in which a programmable circuit connection is selected by toggling the power supply terminal of an IC (VDD) to increment a counter and then once the desired state of the counter is reached so that the desired programmable circuit connection is selected, then the VDD voltage is raised to the programming voltage to programme the selected connection. A disable circuit with a programmable circuit connection is employed to prevent any further accidental programming. There is, however, a need for improved techniques for trimming analogue integrated circuits, in particular power controller integrated circuits.
Other background prior art can be found in: U.S. Pat. Nos. 6,060,899; 5,767,732; and 5,838,076.